1. Field of the Invention
The present invention relates to apparatus and methods for measuring chromatic dispersion.
2. Description of the Background Arts
It is known that the chromatic dispersion of an optical component causes broadening of an incident signal light pulse. Various methods have been examined for precisely measuring chromatic dispersions of optical components in order to evaluate them. Examples of methods for measuring chromatic dispersions of optical components include a time-of-flight method (L. G. Cohen and C. Lin: IEEE J. Quantum Electron. QE-14 (1978) No. 11, p. 855), a modulated signal phase shift method (B. Costa, et al.: IEEE J. Quantum Electron. QE-18 (1982) No. 10, p. 1509), and an interference method (Kazunori Naganuma: NTT R&D vol. 42 (1993) p. 1049). Moreover, a method of measuring the chromatic dispersion by means of four-wave mixing (FWM) is also studied (T. Hasegawa, et al.: OFC2006, paper OTuH5, 2006).
In recent years, much attention has been paid to researches on processing optical signals using FWM that occurs in a highly nonlinear fiber, and various applications are proposed. The highly nonlinear fiber is a fiber in which the efficiency of generating nonlinear phenomenon is enhanced, and in many cases, it is used as a device in which FWM is applied in a length having tens of meters to hundreds of meters.
In such applications, not only the chromatic dispersion (second-order dispersion) but also the higher-order dispersions including dispersion slope and the wavelength dependence of the dispersion slope are important parameters. It is desired that these parameters be considered in the performance evaluation of the highly nonlinear fiber. However, according to the above-mentioned methods of measuring the chromatic dispersion, it has been difficult to achieve a highly precise measurement with respect to the chromatic dispersions of optical components having a length of tens of meters to hundreds of meters. Further problem of such methods is that precisely measuring the chromatic dispersion requires a high-precision phase modulator and a light source having an extremely high degree of wavelength accuracy, for example, and hence a complicated structure.